//----------------------------------------------------------------------
// File:			pr_queue_k.h
// Programmer:		Sunil Arya and David Mount
// Description:		Include file for priority queue with k items.
// Last modified:	01/04/05 (Version 1.0)
//----------------------------------------------------------------------
// Copyright (c) 1997-2005 University of Maryland and Sunil Arya and
// David Mount.  All Rights Reserved.
//
// This software and related documentation is part of the Approximate
// Nearest Neighbor Library (ANN).  This software is provided under
// the provisions of the Lesser GNU Public License (LGPL).  See the
// file ../ReadMe.txt for further information.
//
// The University of Maryland (U.M.) and the authors make no
// representations about the suitability or fitness of this software for
// any purpose.  It is provided "as is" without express or implied
// warranty.
//----------------------------------------------------------------------
// History:
//	Revision 0.1  03/04/98
//		Initial release
//----------------------------------------------------------------------

#ifndef PR_QUEUE_K_H
#define PR_QUEUE_K_H

#include <ANN/ANNx.h>    // all ANN includes
#include <ANN/ANNperf.h> // performance evaluation

//----------------------------------------------------------------------
//	Basic types
//----------------------------------------------------------------------
typedef ANNdist PQKkey;  // key field is distance
typedef int     PQKinfo; // info field is int

//----------------------------------------------------------------------
//	Constants
//		The NULL key value is used to initialize the priority queue, and
//		so it should be larger than any valid distance, so that it will
//		be replaced as legal distance values are inserted.  The NULL
//		info value must be a nonvalid array index, we use ANN_NULL_IDX,
//		which is guaranteed to be negative.
//----------------------------------------------------------------------

const PQKkey  PQ_NULL_KEY = ANN_DIST_INF;  // nonexistent key value
const PQKinfo PQ_NULL_INFO = ANN_NULL_IDX; // nonexistent info value

//----------------------------------------------------------------------
//	ANNmin_k
//		An ANNmin_k structure is one which maintains the smallest
//		k values (of type PQKkey) and associated information (of type
//		PQKinfo).  The special info and key values PQ_NULL_INFO and
//		PQ_NULL_KEY means that thise entry is empty.
//
//		It is currently implemented using an array with k items.
//		Items are stored in increasing sorted order, and insertions
//		are made through standard insertion sort.  (This is quite
//		inefficient, but current applications call for small values
//		of k and relatively few insertions.)
//
//		Note that the list contains k+1 entries, but the last entry
//		is used as a simple placeholder and is otherwise ignored.
//----------------------------------------------------------------------

class ANNmin_k
{
  struct mk_node
  {               // node in min_k structure
    PQKkey  key;  // key value
    PQKinfo info; // info field (user defined)
  };

  int       k;  // max number of keys to store
  int       n;  // number of keys currently active
  mk_node * mk; // the list itself

public:
  ANNmin_k(int max) // constructor (given max size)
  {
    n = 0;                     // initially no items
    k = max;                   // maximum number of items
    mk = new mk_node[max + 1]; // sorted array of keys
  }

  ~ANNmin_k() // destructor
  {
    delete[] mk;
  }

  PQKkey
  ANNmin_key() // return minimum key
  {
    return (n > 0 ? mk[0].key : PQ_NULL_KEY);
  }

  PQKkey
  max_key() // return maximum key
  {
    return (n == k ? mk[k - 1].key : PQ_NULL_KEY);
  }

  PQKkey
  ith_smallest_key(int i) // ith smallest key (i in [0..n-1])
  {
    return (i < n ? mk[i].key : PQ_NULL_KEY);
  }

  PQKinfo
  ith_smallest_info(int i) // info for ith smallest (i in [0..n-1])
  {
    return (i < n ? mk[i].info : PQ_NULL_INFO);
  }

  inline void
  insert(        // insert item (inlined for speed)
    PQKkey  kv,  // key value
    PQKinfo inf) // item info
  {
    int i;
    // slide larger values up
    for (i = n; i > 0; i--)
    {
      if (mk[i - 1].key > kv)
        mk[i] = mk[i - 1];
      else
        break;
    }
    mk[i].key = kv; // store element here
    mk[i].info = inf;
    if (n < k)
      n++;              // increment number of items
    ANN_FLOP(k - i + 1) // increment floating ops
  }
};

#endif
